Safety control for cranes



Aug. 30, 1966 s. G. KNIGHT 3,269,560

SAFETY CONTROL FOR CRANES Filed 060. 28, 1964 2 SheetsSheet 1 INVENTOR SIDNEY 6. KNIGHT was.

Aug. 30, 1966 5. cs. KNIGHT SAFETY CONTROL FOR CRANE'S 2 Sheets-Sheet 2 Filed Dec. 28, 1964 mm Kw INVENTOR SIDNEY 6. KNIGHT BY mfl m @flttys.

United States Patent M 3,269,560 SAFETY CONTROL FOR CRANES Sidney G. Knight, Schofield, Wis., assignor to Drott Manufacturing Corporation, Milwaukee, Wis., a corporation of Wisconsin Filed Dec. 28, 1964, Ser. No. 421,396 Claims. (Cl. 212-39) This invention relates to a safety control for cranes and more particularly to controls for self-propelled cranes having extensible booms.

In the operation of cranes and specifically of self-propelled cranes suspended on wheels or tracks, there are several conditions which can lead to danger of upsetting the crane or damage to portions of the crane mechanism. The first and most common of these conditions is overloading of the crane which could result in overturning thereof with damage to the apparatus and possible injury to the operator or other persons adjacent to the crane. The amount of load which may safely be lifted depends not only on the weight of the load, but also on the length and elevation of the boom which determine the moment arm so that measurement of the load being lifted by the device cannot alone determine when an unsafe condition is being created.

A second condition which occurs arises through excessive elevation of the boom. This could result in moving the load over the apparatus or in bumping and damaging portions of the apparatus by the load as well as damaging of the boom and the lifting mechanism therefor.

A third condition which can arise results if the lifting cable is attempted to be reeled in or if the boom is attempted to be extended further after the load has been raised into contact with the end of the boom. This could easily result in cable breakage or other damage to the apparatus.

It is accordingly an object of the present invention to provide a safety control means for cranes which operates automatically to prevent any of the several different dangerous conditions mentioned above from arising in operation of the crane.

According to a feature of the invention, automatic controls are provided responsive to the degree of extension, angle of elevation of the boom and the load being lifted to control power means which operates to reel in the cable and to elevate the boom to prevent an operation which might tend to produce overturning of the apparatus. In addition, the control means is operated when the load engaging block is raised to the end of the boom to prevent operation of the power means for extending the boom or reeling in the cable.

Another object is to provide safety control means for cranes in which the boom and cable are operated by hydraulic motors and control valves are provided in the connections to the motors to cut off the supply of operating fluid thereto when a dangerous condition is approached. The control valves may be bypassed by check valves which permit operation in a direction to correct the dangerous condition when the control valves are closed.

The above and other objects and features of the invention will be more readily apparent from the following description when read in connection with the accompanying drawings, in which:

FIG. 1 is a side elevation of a self-propelled crane embodying the invention;

FIG. 2 is a view of the control mechanism with parts broken away and in section; and

FIG. 3 is a side elevation with parts broken away and in section of the merchanism for measuring the load on the cable.

The safety control means of the present invention is illustrated as embodied in a self-propelled crane having 3,269,560 Patented August 30, 1966 a frame or chassis 10 supported on wheels 11. A suitable power plant, such as an engine, is carried by the frame or chassis, as indicated at 12, and may be connected to the wheels to drive the same in any desired manner as through either a mechanical or hydraulic transmission.

The vehicle frame carries a crane comprising a base section 13 which is mounted on the frame for rotation about a vertical axis and which extends upwardly from the upper surface of the frame. An extensible boom, indicated generally at 14, is pivoted at the upper end of the base section 13 to swing in a vertical plane. The boom preferably comprises two or more sections, as indicated at 15, 16 and 17 in dotted lines in FIG. 1, which fit telescopically together for extension or retraction to produce any desired length of boom. The boom is preferably con-- trolled hydraulically to extend and contract the same and may be constructed as more particularly described and claimed in my copending application, Serial No. 363,662 filed April 20, 1964, a continuation-in-part of application Serial No. 290,108 filed June 24, 1963, now abandoned.

For picking up a load the outer end of the end boom section 17 carries a fixed block 18 over which a cable 19 is threaded. The cable 19 is threaded over sheaves in a load engaging block 21 which may carry a hook 22 or similar device for engaging and raising a load. The cable 19 is reeled in and out by a drum contained in a housing 23 on the boom so that the load may be raised or lowered, as desired.

The raising and lowering of the boom, the extension and retraction thereof and the reeling in and out of the cable are preferably controlled hydraulically through hydraulic motors, as shown in copending application Serial No. 509,670 filed October 19, 1965, a divisional of the present application. Extension and contraction of the boom is effected through a cylinder and piston type hydraulic motor (not shown) which is preferably mounted in the boom itself. The drum on which the cable is reeled up or from which it is unreeled is driven by a rotary hydraulic motor (not shown). Raising and lowering of the boom is controlled by a cylinder and piston type motor (not shown) which is preferably concealed within the base section or mast 13 so that it is not seen in FIG. 1. The engine on the crane drives a hydraulic pump from which operating fluid is supplied to the several motors and which are provided with manually operated control valves so that the operator can easily and accurately control the several operations of which the boom is capable. The operator may be en closed in a cab 28 within which the controls for movement of the vehicle and for the several operations of the crane itself are housed.

The safety control apparatus of the present invention is preferably enclosed within a housing 29 (FIG. 2) which is mounted on the base section of the boom. This housing may be formed at one side with an indicating scale over which a pointer 31 is movable and which is controlled, as hereinafter described, to indicate the degree of extension of the boom. The tension on the cable 19 is measured by a measuring device 32 (FIG. 3) described more fully hereinafter and which is mounted on the boom, as shown.

The safety control apparatus is more particularly shown in FIG. 2. As there illustrated the degree of extension of the boom is measured by a rotatable drum 33 on which a light cable 34 is wound. The drum is urged to reel up .the cable 34 by a spring 35 and the cable 34 is secured to the end section 17 of the boom so that when the boom is extended the cable will be withdrawn from the drum and will rotate the drum. The cable 34 ment with the stationary block 18. For this purpose, the cable is connected to an electrical wiper 36 which wipes over a conductor disc 37 connected to an electrical lead 38. t

The rotation of the drum 33 is adapted to adjust the angular position of an arm 39 which is pivoted at 41 and which normally extends generally downward from its pivot mounting. For this purpose, the drum is connected through a flexible shaft 42 to a screw 43 which is threaded into a rotatable block 44 on the arm 39, the screw 43 being held against lengthwise movement in a swivel mounting 45 carried by the housing 29. As the screw 43 is turned; it will therefore cause the arm 39 to assume an angular position about the pivot 41 which is proportional to the degree of extension of the boom.

The arm 30 controls the angular position of a second arm 46 which is pivoted at 47 and which is connected into an electrical circuit by a conductor 48. The arm 46 is urged toward the arm 39 by a spring 49 until it engages a cosine cam 51 which is rotatably mounted on the lower end of the arm 39. The angle of the cosine cam is determined by the angle of elevation of the boom, for which purpose a pendulum weight 52 is connected to the pivotal mounting of the cosine cam and will always hang vertically therefrom. Preferably an antifriction roller 53 is carried by the arm 46 to ride against the cam thereby to minimize friction. With this construction, the angle of the arm 46 about its pivotal mounting will be dependent on both the degree of extension and the angle of eleva. tion of the boom. As shown, the pointer 31 is connected to the lower end of the arm 46 through a link 54 to give a visual indication of these conditions.

The load being lifted by the boom is dependent upon the degree of tension in the cable which is measured by the device 32, as best seen in FIG. 3. As shown in this figure, the cable 19 runs over a pair of fixed sheaves 55 which are spaced longitudinally of the cable and is engaged by a third sheave 56 located lengthwise between the two sheaves 55. The sheave 56 is carried by a lever 57 which is pivoted at 58 and whose free end is connected to a link 59 which is connected at its free end to one end of a lever 61. The lever 61 is pivoted intermediate its ends and is connected at its other end to a Bowden cable 62.

As seen in FIG 2, the other end of the cable 62 is connected through a lever 63 to the movable member 65 of a control device which includes a fixed cylinder 64 longitudinally into which the shiftable member 65 fits. The member 65 is connected at one end to an annular plate 66 slidable in the cylinder 64 and which is urged to the right in the cylinder by springs 67. It will be noted from FIG. 2 that a plurality of springs 67 of difierent lengths are provided to become successively effective as the member 65 moved to the left so that any desired characteristic can be obtained in the operation.

The member 65 is connected to a head 68 which is slidable toward and away from the arm 46. Preferably an outer contact portion 69 is slidable in the head 68 and is urged outwardly thereof by a light spring 71 so that in the event of excessive movement the parts will not be damaged. When the outer head portion 69 engages the lever 46 it functions as a switch to complete an electrical circuit between the lead 48 and the lead 72 connected to the head portion 69.

The housing 29 also includes a mercury switch 73 provided with leads 74 and 75 and which is positioned at an angle in the housing, as shown. With the boom in a horizontal, or generally horizontal position the mercury switch will be tipped to a position in which its contacts are open, but as the boom is raised it will eventually raise to an angle at which the mercury will flow lengthwise of the envelope of the switch to complete a circuit therethrough at some predetermined angle. The housing 29 may also carry warning devices, such as a lamp 76 and a buzzer or similar audible signal 77 and similar signals may, if desired, be placed in the operators cab.

Operation of the electrical and hydraulic circuit for manipulation of the boom is described in copending application Serial No. 509,670 filed October 19, 1965.

With respect to operation of switch 73, it will be noted in this connection that elevation of the boom would tend to raise the load and would contribute to the unsafe condition while lowering of the boom would lengthen the moment arm of the load also increasing the tendency to overturn the crane. It is desirable when an overload is encountered to prevent any movement of the boom in either direction.

If the boom should be raised to the desired maximumupper limit the mercury switch 73 would be tilted in a direction to close its contacts which through circuitry described in the aforementioned copending application prevent further movement of the boom.

While one embodiment of the invention has been shown and described herein, it will be understood that it is illustrative only and not to be taken as a definition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

1. Safety control means for cranes in combination with a crane having an extensible and vertically swingable boom, power means to extend the boom, second power means to swing the boom vertically, and means at the outer end of the boom to engage and lift a load, the safety control means comprising a first movable member mounted on the boom, means responsive to extension of the boom to adjust the position of the first movable member, a cam movably mounted on the first movable member, gravity responsive means to maintain the cam in a predetermined position relative to vertical, a second movable control member, means to maintain the second control member in engagement with the cam, a third movable control member, means responsive to the load on the boom to move the third control member toward and away from the second control member, and means operated by engagement of the third control member with the second control member to prevent operation of the power means to extend or elevate the boom.

2. Safety control means for cranes in combination with a crane having an extensible and vertically swingable boom, power means to extend the boom, second power means to swing the boom vertically, a cable extending from the end of the boom, a load engaging device carried by the cable to connect to a load, third power means connected to the cable to reel the same in and out thereby to raise and lower the load engaging device, the safety control system comprising a first movable member mounted on the boom, a cam movably mounted on the first control member, means responsive to extension of the boom to adjust the position .of the first control member, means to maintain the cam in a predetermined angular position relative to vertical, a second movable control member movable toward and away from the cam, means to maintain the second control member in engagement with the cam, a third movable control member, means responsive to the tension in the cable to move the third control member into engagement with the second control member, and means operated by engagement of the second and third control members to prevent operation of the power means to extend or elevate the boom or to reel in the cable.

3. The apparatus of claim 2 including means responsive to movement of the load engaging device to a position closely adjacent to the end of the boom to prevent operation of the power means to extend the boom or reel in the cable.

4. Safety control means for cranes in combination with a crane having an extensible and vertically swingable boom, power means to extend the boom, second power means to elevate and swing the boom vertically, and

means at the outer end of the boom to engage and lift a load, the safety control means comprising a first movable member, means responsive to extension of the boom to adjust the position of said first movable member, a cam pivotally mounted on said first movable member, means to maintain the cam in a predetermined position relative to vertical by pivoting relative to said first member, a second movable member in engagement With said calm, a third member movable toward and away firom said second movable member in response to the load on the boom, and means operated when said third member has moved to a predetermined position relative to said second member to prevent operation of the power means to extend or elevate the boom.

5. The safety control means of claim 4 including second control means responsive to elevation of the boom to prevent operation of the second power means in a direction to elevate the boom further.

References Cited by the Examiner UNITED STATES PATENTS White 212-39 Harry 212-21 Bowerman 212-21 Nowack 212-39 Kuhlenschmidt et a1. 212-35 Aitken 212-39 X Aitken 212-39 X Province 212-35 Vermes 212-39 Germany.

EVON C. BLUNK, Primary Examiner.

A. L. LEVINE, Assistant Examiner. 

1. SAFETY CONTROL MEANS FOR CRANES IN COMBINATION WITH A CRANE HAVING AN EXTENSIBLE AND VERTICALLY SWINGABLE BOOM, POWER MEANS TO EXTEND THE BOOM, SECOND POWER MEANS TO SWING THE BOOM VERTICALLY, AND MEANS AT HE OUTER END OF THE BOOM TO ENGAGE AND LIFT A LOAD, THE SAFETY CONTROL MEANS COMPRISING A FIRST MOVABLE MEMBER MOUNTED ON THE BOOM, MEANS RESPONSIVE TO EXTENSION OF THE BOOM TO ADJUST THE POSITION OF THE FIRST MOVABLE MEMBER, A CAM MOVABLY MOUNTED ON THE FIRST MOVABLE MEMBER, GRAVITY RESPONSIVE MEANS TO MAINTAIN THE CAM IN A PREDETERMINED POSITION RELATIVE TO VERTICAL, A SECOND MOVABLE CONTROL MEMBER, MEANS TO MAINTAIN THE SECOND CONTROL MEMBER IN ENGAGEMENT WITH THE CAM, A THIRD MOVABLE CONTROL MEMBER, MEANS RESPONSIVE TO THE LOAD ON THE BOOM TO MOVE THE THIRD CONTROL MEMBER TOWARD AND AWAY FROM THE SECOND CONTROL MEMBER, AND MEANS OPERATED BY ENGAGEMENT OF THE THIRD CONTROL MEMBER WITH THE SECOND CONTROL MEMBER TO PREVENT OPERATION OF THE POWER MEANS TO EXTEND OR ELEVATE THE BOOM. 